Ring hole planning for external fixation frames

ABSTRACT

An external fixation system includes first and second fixation members having first and second pluralities of mounting holes, respectively. The first and second plurality of holes are configured to receive first and second ends of a plurality of struts, each strut having a default or initial mounting position. A simulation of the correction may be performed with the struts in the default positions, but it may be determined that the correction is not achievable. Additional simulations of the correction may be performed with the ends of the struts in different mounting positions to determine if other mounting positions of the struts allow the correction to be completed. During the correction, if one of the struts reaches a maximum length, it may be disconnected and reconnected to a different mounting hole so that, after being reconnected, the strut may be further increased in length to continue the correction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/383,585, filed Jul. 23, 2021, which is a continuation of U.S. Pat.No. 11,083,495, filed Apr. 9, 2018, which is a continuation of U.S. Pat.No. 10,010,346, filed Apr. 20, 2016, the disclosures of which are herebyincorporated by reference herein.

BACKGROUND OF THE DISCLOSURE

Many different types of bone deformities can be corrected using externalfixation systems to perform the distraction osteogenesis process. Forexample, an Ilizarov device or similar external fixation system may beused. Such systems generally use rings, also designated as fixationplates, connected to one another by threaded rods or struts. Each ringis coupled to the bone of interest at opposite ends of a deformity. Thelengths of the struts are adjusted over time to change the position andorientation of the two rings with respect to one another, which in turnrepositions and reorients the bone fragments, with a goal of correctingthe bone deformity.

Each strut is attached to a position, usually a hole or other aperture,on each of the rings at the beginning of the correction procedure. Asthe strut lengths are changed and the correction procedure continues,the mounting locations between the struts and the frames generallyremain constant. The initial mounting locations of the struts to therings may limit the maximum range of motion between the rings, and thuslimit the ability to correct certain severe deformations. However,external fixation rings systems generally include default mountinglocations for the struts. The ability to mount struts to positions onthe rings other than the default positions may be limited. For example,mounting struts to positions on the rings other than the defaultpositions may lead to relatively large strut angles that reduce thestability of the fixation frame construct.

BRIEF SUMMARY

According to one aspect of the disclosure, an external fixation systemincluding a first fixation member having a first plurality of mountingholes each configured to receive a first end of one of a plurality ofstruts and a second fixation member having a second plurality ofmounting holes each configured to receive a second end of one of theplurality of struts. Each strut has a default mounting positioncorresponding to one of the holes in each of the first and secondfixation members. A method of establishing mounting positions of aplurality of struts in an external fixation system includes performing afirst simulation of a correction of a bone deformity with the first andsecond ends of the plurality of struts coupled to the first and secondfixation members in the default mounting position. A second simulationof a correction of a bone deformity is performed with the first end ofone of the plurality of struts coupled to the first fixation member in afirst alternative mounting position, wherein in the first alternativemounting position the first end of the one strut is located in a holedifferent from the default mounting position. It may then be determinedwhether the correction of the bone deformity is achievable based on thefirst and second simulations. The first end and second end of each ofthe plurality of struts may be mounted to the first and second fixationmembers in the default mounting position.

It may then be determined that the correction of the bone deformity isnot achievable based on the first simulation. One of the plurality ofstruts may be identified as a problem strut resulting in the correctionof the bone deformity being not achievable. In the first alternativemounting position in the second simulation, the first end of the problemstrut may be coupled to the first fixation member at one of the mountingholes directly adjacent the default mounting position in a firstdirection. A third simulation of the correction of the bone deformitymay be performed wherein the first end of the problem strut is coupledto the first fixation member at one of the mounting holes directlyadjacent the default mounting position in a second direction oppositethe first direction in a second alternative mounting position. It may bedetermined that the correction of the bone deformity is not achievablebased on the second and third simulations; and a problem strutconstraint causing the correction of the bone deformity to beunachievable may be determined. It may also be determined which of thefirst alternative mounting position and second alternative mountingposition provides greater alleviation of the problem strut constraint.

It may be determined that the first alternative mounting positionprovides greater alleviation of the problem strut constraint. A fourthsimulation of the correction of the bone deformity may be performed withthe problem strut in a third alternative mounting position in which thefirst end of the problem strut is coupled to the first fixation memberin a mounting hole directly adjacent the first alternative mountingposition in the first direction.

It may be determined that the correction of the bone deformity is notachievable based on the fourth simulation. A fifth simulation of thecorrection of the bone deformity may be performed with the problem strutin a fourth alternative mounting position in which the first end of theproblem strut is coupled to the first fixation member in a mounting holedirectly adjacent the third alternative mounting position in the firstdirection.

It may be determined that the correction of the bone deformity is notachievable based on the fifth simulation. A sixth simulation of thecorrection of the bone deformity may be performed with the problem strutin a fifth alternative mounting position in which the second end of theproblem strut is coupled to the second fixation member in a mountinghole directly adjacent the default mounting position in the seconddirection.

It may be determined that the correction of the bone deformity is notachievable based on the sixth simulation. A seventh simulation of thecorrection of the bone deformity may be performed with the problem strutin a sixth alternative mounting position in which the second end of theproblem strut is coupled to the second fixation member in a mountinghole directly adjacent the fifth alternative mounting position in thesecond direction.

It may be determined that the correction of the bone deformity is notachievable based on the seventh simulation. An eighth simulation of thecorrection of the bone deformity may be performed with the problem strutin a seventh alternative mounting position in which the second end ofthe problem strut is coupled to the second fixation member in a mountinghole directly adjacent the sixth alternative mounting position in thesecond direction.

The method may include beginning to perform the correction of the bonedeformity by increasing a length of at least one of the plurality ofstruts. The correction of the bone deformity may be continued until theone strut reaches a maximum length. The first end of the one strut maybe disconnected from the default mounting position and reconnected to ahole in the first fixation member different than the default mountingposition. The correction of the bone deformity may be completed.

According to another aspect of the disclosure, an external fixationsystem includes a first fixation member having a first plurality ofmounting holes each configured to receive a first end of one of aplurality of struts and a second fixation member having a secondplurality of mounting holes each configured to receive a second end ofone of the plurality of struts. A method of correcting a bone deformitywith the external fixation system includes fixing the first fixationmember to a first bone segment and fixing the second fixation member toa second bone segment. A first end of each of the plurality of struts iscoupled to one of the first plurality of mounting holes of the firstfixation member and a second end of each of the plurality of struts iscoupled to one of the second plurality of mounting holes in the secondfixation member, each of the plurality of struts being in an initialmounting position. The correction of the bone deformity may be begun byincreasing a length of at least one of the plurality of struts, with thecorrection being continued until the one strut reaches a maximum length.The first end of the one strut may be disconnected from the initialmounting position and reconnected to one of the first plurality of holesin the first fixation member different than the initial mountingposition. The correction of the bone deformity may be completed.

A position of the first fixation member may be fixed with respect to thesecond fixation member prior to disconnecting the first end of the onestrut from the initial mounting position. The step of fixing theposition of the first fixation member with respect to the secondfixation member may include clamping the first and second fixationmembers.

The length of the one strut may be decreased after disconnecting thefirst end of the one strut from the initial mounting position but beforereconnecting the first end of the one strut to one of the firstplurality of holes in the first fixation member different than theinitial mounting position. The step of completing the correction of thebone deformity may include increasing the length of the one strut afterreconnecting the first end of the one strut to one of the firstplurality of holes in the first fixation member different than theinitial mounting position. The second end of the one strut may remain inthe initial mounting position throughout the correction of the bonedeformity. The same plurality of struts may couple the first fixationmember to the second fixation member during the correction of the bonedeformity without introducing a new strut to the external fixationsystem. The first and second fixation systems may each be rings having afirst inner circumferential row of holes and a second outercircumferential row of holes, the initial mounting position beingrespective ones of the second outer circumferential rows of holes. Holesin the first inner circumferential row may be circumferentiallystaggered (i.e. not radially aligned) with respect to holes in thesecond outer circumferential row.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an external fixation frame.

FIG. 2 is a graph showing maximum angulation of the external fixationframe of FIG. 1 for default strut mounting positions compared to certainalternate potential strut mounting positions.

FIG. 3 is a flow chart of a method according to an aspect of thedisclosure.

FIG. 4A is an example of a display image showing struts in defaultpositions in according with an aspect of the disclosure.

FIG. 4B is an example of a display image showing struts in defaultpositions with at least one strut in a non-default position.

FIG. 4C illustrates a display of an external fixation system with thestrut configurations of FIG. 4A.

FIG. 4D illustrates a display of an external fixation system with thestrut configuration of FIG. 4B.

FIG. 5A is a schematic view of the external fixation frame of FIG. 1with one strut at a maximum length.

FIG. 5B is a schematic view of the external fixation frame of FIG. 5Aafter repositioning one of the struts.

FIG. 6A is a perspective side view of an external fixation frameaccording to another aspect of the disclosure.

FIG. 6B is a perspective top view of the external fixation frame of FIG.6A.

DETAILED DESCRIPTION

FIG. 1 shows an external fixation frame 10 in an assembled conditionaccording to one aspect of the disclosure. Generally, fixation frame 10includes a first ring 20 and a second ring 30, with six telescopicstruts 40 a-f coupling the first ring 20 to the second ring 30. Thefirst ring 20 may also be referred to as a proximal ring or a referencering, while the second ring 30 may also be referred to as a distal ringor a moving ring. In the illustrated embodiment, each strut 40 a-fincludes a threaded portion that may thread into or out of a shaftportion to decrease or increase the length, respectively, of thetelescopic strut. Each end of each strut 40 a-f may be coupled to thefirst ring 20 and second ring 30 via a joint mechanism, such as a balljoint, a constrained hinge joint, or a universal joint as illustrated.The use of universal joints on each end of the strut provides for sixdegrees of freedom of motion of the external fixation system 10. Variousmechanisms may be employed to adjust the lengths of the struts 40 a-f.For example, in the illustrated embodiment each strut 40 a-f is coupledto the first ring 20 via an actuator that extends proximally of thefirst ring 20. A user may engage a tool, such as a screwdriver typetool, to rotate the actuator to in turn increase or decrease the lengthof the particular strut 40 a-f. It should be understood that althoughthe disclosure is generally described in the context of closed circularrings, the concepts described herein may apply with equal force to othertypes of rings, such as open rings and/or U-shaped rings.

The first fixation ring 20 and second fixation ring 30 may each includea plurality of holes or apertures extending from a top surface to bottomsurface of each fixation ring. For example, the first fixation ring 20and second fixation ring 30 may each include fifty two holes spacedevenly around the circumference of the ring. In one convention, theholes are numbered from zero through fifty-one in a clockwise directionalong the fixation rings 20, 30. The fixation rings 20 and 30 mayinclude markings or other indicia adjacent certain holes in the fixationframes that correspond to desired default mounting positions for thedifferent struts 40 a-f. In the example of rings 120 and 130 describedin greater detail below in connection with FIGS. 6A-B, the defaultmounting positions may be the centermost holes in the outercircumferential row 170 of each extension tab 150 (see FIG. 6B).

In some circumstances, it may be desirable to attach struts 40 a-f tothe first and second fixation frames 20, 30 at mounting locationsdifferent than the default mounting positions. In one example, there maybe other components of the external fixation system 10 that wouldinterfere with the position of the struts 40 a-f. Such components couldinclude K-wires, mounting posts, bone pins, or any other featureattached to either the first ring 20 or second ring 30, including thosecoupling portions of the fixation frame 10 to the patient's bone. Theposition of these components may be dictated by the particular surgicalsituation and there may be little leeway to shift the position of thesecomponents, so it may be preferable or necessary to reposition themounting position of the struts 40 a-f to avoid interference with thoseother components. Besides potential interference with components offixation system 10, the struts 40 a-f may also interfere with soft orhard tissue of the patient if the default mounting positions are used.

In another example, in severe deformities, given a fixed range ofdistance between the first ring 20 and second ring 30, achieving adesired correction with struts 40 a-f coupled to the first and secondrings 20, 30 at the default mounting positions may be impossible. It wasdetermined that changing the mounting positions of the struts 40 a-ffrom the default mounting positions may increase the maximum achievableangulation. FIG. 2 illustrates a graph of maximum achievable angulationin a three strut external fixation system (provided in degrees on they-axis) versus the distance between the top and bottom rings of thefixation system (provided in millimeters on the x-axis). In FIG. 2 , thesolid line represents an external fixation system in which struts areattached at default positions, whereas the dotted line represents thesame system in which the struts may have their initial mounting positionshifted up to three holes in the clockwise or counterclockwisedirection. As can be seen in FIG. 2 , it was found that the fixationframe can achieve a significantly greater degree of angulation when thestruts are allowed to have an initial mounting position shifted up tothree holes in the clockwise or counterclockwise direction from thedefault position.

A series of method steps may be implemented to determine the optimumlocation of mounting locations for struts to the fixation frame rings.The below steps are one example for a system with three struts, similaror identical to any of struts 40 a-f, and at least two fixation rings,similar or identical to rings 20 and 30. However, it should beunderstood that the method may also be used with other systems,including the six strut external fixation systems 10 and 110 of FIGS. 1and 6A, respectively. For a three-strut system for use with rings 20 and30 having fifty-two holes each, the default mounting locations for thethree struts may be set as 0, 16, and 36 for each ring with thenumbering being provided in a clockwise direction, beginning with 0 andending in 51. For example, a first strut may have a default mountingposition of hole 0 on both the first and second rings 20, 30, a secondstrut may have a default mounting position of hole 16 on the first andsecond rings 20, 30, and a third strut may have a default mountingposition of hole 36 on the first and second rings 20, 30. In a firststep, as shown in FIG. 3 , a determination is made whether thethree-strut system mounted at the default holes (0, 16, and 36 of eachring) is sufficient to achieve the desired correction. Such adetermination may be made using planning software known in the art whichis capable of simulating the desired correction using virtual fixationcomponents corresponding to the actual fixation components and a virtualbone model corresponding to the patient's actual bone. If the desiredcorrection may be achieved with this configuration, the default mountingpositions should be used. If the desired correction cannot be achieved,the strut restricting the ability for the system to achieve the desiredcorrection is determined, for example as an output of the software. Thedefault mounting positions may be particular to the particular externalfixation frame. For example, and as noted above, for the fixation system110 shown in FIGS. 6A-B and described in greater detail below, thedefault mounting positions may be the center two holes in the outercircumferential row 170 of each extension tab 150 for each ring 120,130.

Still referring to FIG. 3 , the correction is then simulated two moretimes with the strut causing the limitation being in an initial mountingposition on the first ring 20 shifted by one hole in the clockwisedirection ([1, 16, 36] for the top ring 20) and shifted one hole in thecounterclockwise direction ([51, 16, 36] for the top ring 20). If eitherof the two revised initial mounting positions provides the ability toachieve the desired correction, the revised initial mounting positionshould be used to perform the correction. If neither of the two revisedinitial mounting positions provide the ability to achieve the desiredcorrection, it should be determined which of the simulated revisedpositions eases the constraint causing the problem. For example, if thefirst strut is limiting the ability to achieve the desired correctionbecause the strut angle is too extreme at some point in the correctionprocess, and the modified mounting position of +1 (at hole 1) causes theangle to increase in extremity and the modified mounting position of −1(at hole 51) causes the angle to decrease in extremity, anothercorrection simulation should be performed with the initial mountingposition modified another hole in the direction that eases theconstraint, in this case in the negative or counterclockwise direction.In other words, at this point another simulation would be performed withthe initial mounting position of the first strut at [2, 16, 36] for thetop ring 20. If the correction is achievable with this mountingposition, it should be used to achieve the correction. If the relevantconstraint is still violated, the simulation is performed one more timewith the problematic strut shifted one more hole in the same direction,which in this example would be at [3, 16, 36] for the top ring 20.Again, if the correction is achievable in this third revised position,the third revised position should be used to achieve the correction.However, if shifting the strut three holes in the first ring 20 (eitherin the clockwise or counterclockwise direction depending on whichdirection eases the constraint) does not allow the correction to beachieved, the mounting position of the strut is moved in the oppositedirection one hole on the second or bottom ring 30, and the correctionis simulated again. In this example, if the mounting position [3, 16,36] for the top ring 20 and [0, 16, 36] for the bottom ring 30 stilldoes not allow the desired correction to be achieved, the mountingposition of the first strut on the bottom ring 30 is moved in theopposite direction one hole to [51, 16, 36] and the correction issimulated again. This process is repeated until a suitable mountingposition is found that allows the correction to be achieved, orotherwise until a maximum of three position shifts have been attemptedon the first ring in the first direction and three position shifts havebeen attempted for the same strut on the second ring in the secondopposite direction. If three position shifts for the problem strut aresimulated on each ring, in this case to a maximum of [3, 16, 36] for thetop ring 20 and [49, 16, 36] for the bottom ring, and the correction isstill not able to be achieved, a determination is made that thecorrection cannot be achieved using the external fixation frame. Itshould be understood that although the method above is described interms of first changing the mounting positions of the top ring 20 andthen subsequently changing the mounting positions of the bottom ring 30,this order does not need to be strictly followed. However, changing themounting position of strut on the top ring 20 generally leads to a moreprominent angle change than a corresponding mounting position change inthe bottom ring 30, so it is preferable to attempt first, second, andthird mounting position shifts, if necessary, in the top ring 20 beforebeginning to change the mounting positions of a strut to the bottom ring30. Although the constraint is generally described herein as strut angleor length constraints, other relevant constraints include a strutcausing undesirable visibility or if the strut is in the way of otherfixation frame components, such as points of wire fixation or apex pinsof the system.

In order to assist a surgeon in carrying out the above process, it ispreferable that the surgeon is provided with an intuitive softwareinterface to assist in the determinations. For example, the surgeon maybe provided with a display operatively connected to a computer systemwith one or more associated processors and memories, with the softwarebeing stored on one of the associated memories and with the operation ofthe software assisted by one or more of the associated processors. FIG.4A illustrates an image that may be displayed by the software on adisplay accessible to the surgeon, the image including a top view of theproximal or top ring 20 of the external fixation system 10 of FIG. 1 anda top view of the distal ring or bottom ring 30 of the external fixationsystem 10 of FIG. 1 . The images of top ring 20 and bottom ring 30 mayindicate default mounting positions of struts 40 a-f by providing anindicator within the particular hole of the ring that the strut isintended to be mounted in the default position. For example, the defaultmounting position of each strut 40 a-f may be indicated by a colorfilling the corresponding default mounting hole within the image of thehole provided on the display, with each strut corresponding to a uniquecolor. As can be seen in FIG. 4A, other indicia may be provided on theimage of the top and bottom rings 20, 30 to indicate default mountingpositions. For example, shapes such as triangles or rectangles may beprovided directly on the rings 20, 30 to indicate where the defaultmounting positions are. It should be understood that similar oridentical indicia may be printed or otherwise provided on the physicalrings themselves. In the illustrated example, triangle shapes areprovided adjacent particular holes on the top and bottom ring 20, 30.For a six strut system, the triangle shapes indicate that the defaultposition of one strut is on a first side of the indicator and thedefault position of another strut is on the other side of the indicator,with a total of three indicators on each rings indicating the defaultmounting position of six struts in all. For a three strut system, thetriangles correspond directly to the default hole mounting positions.Other indicators, such as the square indicator shown, may indicate afour strut system.

With the struts 40 a-f displayed on top ring 20 and bottom ring 30 indefault positions, a user may click or otherwise select a particularstrut on the display, and upon selecting that strut, additional possiblemounting positions of the strut may be illustrated or otherwiseindicated. For example, in FIG. 4A, the first strut 40 a is shown in itsdefault position, with the two holes immediately adjacent the firststrut 40 a default hole in the counterclockwise direction (as viewedfrom above) highlighted as potential alternate positions. Similarly, forthe first strut 40 a in the second or bottom ring 30, two strut holesimmediately adjacent the first strut 40 a default hole in the clockwisedirection (as viewed form above) are highlighted as potential alternatepositions. Upon performing a simulation of the correction, if thedefault positions of struts 40 a-f allow for the correction to beachieved, the default positions may be used for the correction. Itshould be understood that the number of maximum hole offsets may dependon the particular fixation system, but generally a maximum number ofhole offsets of two or three may be suitable.

FIG. 4B illustrates the displayed image in FIG. 4A after it wasdetermined that the fixation system 10 could not achieve the desiredcorrection with the second strut 40 b in the default position. As shownin FIG. 4B, the user, after selecting the second strut 40 b, potentialalternate mounting holes for second strut 40 b were highlighted orotherwise indicated to the user. By selecting the desired revisedmounting hole for second strut 40 b, for example by clicking the desiredhole among the alternate options presented, the mounting position of thesecond strut 40 b changes. In FIG. 4B, the mounting position of thesecond strut 40 b in the top ring 20 was shifted two holes in thecounterclockwise direction, with the mounting position of the secondstrut 40 b in the bottom ring 30 shifted two holes in the clockwisedirection.

The software may also update a model of the fixation system 10 each timethe user shifts the mounting hole(s) of a strut 40 a-f to provide thesurgeon a view of the fixation system 10. For example, FIG. 4Cillustrates a perspective view of fixation frame 10 with top ring 20coupled to a first bone fragment F1 and bottom ring 30 coupled to asecond bone fragment F2, with struts 40 a-f in their default mountingpositions of FIG. 4A. After the user changes the mounting positions ofsecond strut 40 b from the default positions two holes counterclockwisein the top ring 20 and two holes clockwise in the bottom ring 30, asshown in FIG. 4B, the display of the fixation frame may update, as shownin FIG. 4D, to show the user what the fixation frame 10 would look likewith the updated strut positions. This may help the user confirm, forexample, that a strut such as strut 40 b has a more stable angle in theupdated fixation frame 10 configuration of FIG. 4D compared to thedefault fixation frame 10 configuration of FIG. 4C.

Another potential issue that arises during the course of correction of abone using fixation frame 10 is the potential necessity of a strutchange-out. As noted above, during the correction process, one or moreof the telescopic struts 40 a-f are increased in effective length bythreading the threaded rod portion of the strut out of the shaft to movea first end of the strut away from the opposite end of the strut,effectively increasing the effective length of the strut. Struts oftencome in standard sizes, such as small struts, medium struts, and largestruts, the struts being generally classified by a maximum achievableeffective length. During the correction procedure, a particulartelescopic strut may be extended to its maximum effective length (oralternatively shortened to its minimum effective length), prior tocompleting the correction procedure. In a case where a telescopic strutreaches its maximum effective length prior to finishing the correctionprocedure, the patient often needs to go the appropriate medicalpersonnel to have the strut replaced with a larger strut capable of agreater effective length than the strut that reached its maximumeffective length. In order to complete this procedure, the first frame20 and second frame 30 must generally be fixed in position with respectto one another and the bone, for example using a clamp system to attachto both rings 20 and 30 and to constrain the system in every degree offreedom so that up to five of the six struts may be removed withoutaltering the position and orientation of the rings. The strut at itsmaximum effective length is removed from the fixation frame 10, and thenew larger strut is coupled to the fixation frame in the same mountingpositions as the removed strut. It should be understood that althoughthe method described herein is provided relative to eliminating the needfor a strut change-out to a larger strut after a strut reaches itsmaximum effective length, the concepts would apply to eliminating theneed for a strut change-out to a smaller strut after a strut reaches aminimum effective length.

As should be understood, the requirement of one or more additionalstruts to complete the correction procedure may increase the complexityand particularly the overall cost of the procedure. As an alternative tochanging out a strut after the strut reaches its maximum effectivelength, the mounting position of the strut may be changed with respectto one or both fixation rings using the same strut. If the distancebetween the new mounting holes is less than the distance between thecurrent mounting positions where the strut is at its maximum effectivelength, the new mounting position will provide the ability for the strutto further increase in length so that the correction may be completed.This ability is provided by the new angle between the strut and thefixation rings. FIGS. 5A-B illustrate the above method, but it should beunderstood that the components of external fixation system 10 are notnecessarily provided to scale.

In FIG. 5A, fixation frame 10 is shown with six struts 40 a-f couplingthe top ring 20 to the bottom ring 30, with strut 40 c having beenincreased in length to its maximum possible effective length. It shouldbe understood that generally, rings 20 and 30 would not be parallel atthis point in the correction, but are shown to be parallel merely forsimplicity. Strut 40 c is coupled to a first hold on the top ring 20 anda second hole on the bottom ring 30, with a distance of D₁ being betweenthe respective holes. If the correction called for a further increase inlength of strut 40 c, the correction would not be able to be completedwith strut 40 c remaining in the position shown in FIG. 5A.Traditionally, strut 40 c would be replaced with a larger strutconnecting to the same holes that strut 40 c is shown connected to inFIG. 5A. However, to avoid the need to use another strut, anothersolution is to connect strut 40 c to different holes on the top ring 20and/or bottom ring 30 to allow strut 40 c to continue to cause movementof rings and 30 with respect to one another. Because strut 40 c is atits maximum effective length when coupled to holes in the top ring 20and bottom ring 30 having a distance D₁, the strut 40 c may be connectedto a different hole in the top ring 20, a different hole in the bottomring 30, or both, so long as the new hole positions are at a distancefrom one another less than D₁. In other words, as long as the angle ofthe strut 40 c between the first ring 20 and second ring 30 transitionscloser to being perpendicular the top ring 20, the strut 40 c will beable to provide for additional correction.

As shown in FIG. 5A, strut 40 c may be kept fixed to the originalmounting hole in the bottom ring 30, with the strut 40 c rotated in thedirection R so that the top of strut 40 c connects to a new mountinghole. To accomplish this, rings 20 and 30 would be clamped with respectto one another by medical personnel and strut 40 c detached from atleast the top ring 20. Strut 40 c would then need to be shortened adegree because the distance between the new mounting holes D₂, as shownin FIG. 5B, is less than the original distance D₁ between the originalmounting holes. With the clamps keeping rings 20 and 30 fixed in theiroriginal position, and with the strut 40 c shortened from its maximumeffective length, the medical personnel couple the top of strut 40 c tothe new mounting hole in top ring 20. Because strut 40 c needed to beshortened to make the new connection between rings 20 and 30, it becomesavailable to continue lengthening via the telescopic action describedabove to further reposition ring 20 with respect to ring 30. Once theclamps are removed, the correction may continue. It should be understoodthat although a single strut 40 c is illustrated as having only one ofits mounting hole positions changed, one or more struts 40 a-f may havetheir positions change to avoid the requirement of adding new struts tothe system, and the new position may be only a new mounting hole in thetop ring 20, only a new mounting hole in the bottom ring 30, or newmounting hole positions for both the top and bottom rings 20, 30.Assuming a strut 40 a-f reaches its maximum effective length prior tothe correction procedure being completed, the only requirements forchanging strut position are that (a) the distance between the new holemounting positions is less than the distance between the previous holemounting positions, and (b) the correction is achievable with the strutin the new mounting positions. If the method is being used to repositiona strut after it has reached its minimum effective length, the distancebetween the new hole mounting positions must be greater than thedistance between the previous hole mounting positions.

The concepts described above may be applied to other fixation systemswith other types of rings. For example, FIGS. 6A-B illustrate anexternal fixation system 110 according to an aspect of the disclosure.External fixation system 110 is generally similar to external fixationsystem 10 with certain difference. External fixation system 110 includesa top ring 120 and a bottom ring 130 coupled to one another by aplurality of telescopically extending struts 140 a-140 f similar toexternal fixation system 10, However, unlike rings 10 and 20, rings 120and 130 include a plurality of extension tabs 150, as best seen in FIG.6B. In the illustrated example, each ring 120 and 130 includes sixextension tabs 150 spaced circumferentially around the perimeter of therespective rings, although more or fewer may be suitable depending onthe particular components of the fixation system. In addition to what isdescribed directly below, extension tabs 150 may help increase thecross-sectional area of rings 120, 130 and thus provide for increasedstiffness of the rings.

With this configuration, each ring 120, 130 includes a first innercircumferential row of holes 160 and a second outer circumferential rowof holes 170. As illustrated, the second outer circumferential row ofholes 170 may be only positioned on the plurality of extension tabs 150on the rings 120 and 130. It should be understood that although thesecond outer circumferential row of holes 170 is shown in FIGS. 6A-B asbeing positioned solely on extension tabs 150, top ring 120 and/orbottom ring 130 may contain two complete rows of holes, for example witha completely circular (or nearly completely circular) geometry. The useof extension tabs 150, compared to two full circumferential rows ofholes, may help reduce overall bulk of rings 120, 130 and also providefor intuitive strut placement for surgical personnel. The completelycircular version of rings 120, 130 with two full (or nearly full) rowsof circumferential holes may be particularly suited for relatively smalldiameter rings, although indentations or other features may beintroduced to provide an intuitive interface for strut placement bysurgical personnel. Further, in the illustrated embodiment, the firstand second circumferential rows of holes 160 and 170 are positioned sothat the first row of holes 160 does not align radially with the secondrow of holes 170. In other words, the first row of holes 160 has astaggered configuration with respect to the second row of holes 170.With struts 140 a-f initially coupled to holes in the secondcircumferential row 170 on extension tabs 150 in the top and bottomrings 120 and 130, the correction may proceed until it is complete oruntil one or more of the struts 140 a-f reaches its maximum effectivelength. Similar to the description above in connection with FIGS. 5A-B,the rings 120 and 130 may be clamped or otherwise fixed if one or morestruts 140 a-f reach their maximum effective lengths, and whicheverstrut(s) 140 a-f is at a maximum length may be disconnected from one orboth rings 120, 130, and recoupled to another hole or holes to increasethe maximum effective length of the strut. The strut 140 a-f at itsmaximum length may be coupled to circumferentially adjacent hole 170 ata less acute angle similar to described in connection with FIGS. 5A-B.Alternatively, the strut 140 a-f at its maximum length may be connectedto a hole in the first circumferential row 160 of the top and/or bottomrings 120, 130. The presence of two rows of circumferential holes 160and 170 in a staggered configuration may provide more options forreconnecting a particular strut 140 a-f to effectively increase therange of length of the strut while being able to maintain the plannedtrajectory of the rings 120 and 130 during the deformity correctionprocess. The additional hole options may also be utilized for connectingother components, such as fixation pins to couple the rings 120, 130 tothe respective bone fragments. Still further, the staggeredconfiguration of holes between the first and second rows 160, 170 mayalso help prevent interference between components attached to nearbyholes, for example such as a strut positioned in a first hole and afixation pin or other fixation member attached to an adjacent or nearbysecond hole. For example, a relatively thin wire extending radially fromone of the holes in the first circumferential row 160 may not radiallyinterfere with a hole positioned in the second circumferential row 170because of the radial staggering. It should be understood that the sizeof the tabs 150 may increase or decrease depending on the diameter ofthe rings 120 and 130, with greater diameter rings 120 and 130 havinglarger tabs 150 with more holes 170 compared to smaller diameter rings.For example, the illustrated tabs 150 include six holes 170, and asmaller ring may include smaller tabs with four holes each, for example.Regardless of the size of the particular ring and corresponding tab, thestagger pattern of the holes in the first and second circumferentialrows may be maintained. In addition to the benefits described above, theconcepts provided herein may allow for less complex struts compared toan external fixation system that uses more expensive and complex struts,for example a double telescoping strut system, to solve the problem ofstrut change-outs when a strut reaches its maximum effective length.

Finally, it should be understood that the concepts and methods describedabove regarding the choice of initial mounting positions for struts inan external fixator system may be used with or without the concepts andmethods described in relation to changing the mounting position of oneor more struts during the progression of the correction itself.Similarly, the concepts and methods described in relation to changingthe positions of one or more struts mid-correction may be used with orwithout the concepts described above regarding the choice of initialmounting positions for the struts.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A method of ring hole planning for an external fixation frame, themethod comprising: displaying on a display device a first virtualfixation ring including a plurality of virtual holes, the first virtualfixation ring corresponding to a first physical fixation ring, theplurality of virtual holes corresponding to a plurality of physicalholes in the first physical fixation ring; displaying on the displaydevice a first portion of a virtual strut positioned within a first oneof the virtual holes in a virtual default strut mounting position,wherein the virtual strut corresponds to a physical strut; the firstvirtual hole corresponding to a first one of the physical holes, thefirst physical fixation ring including an indicator adjacent to thefirst physical hole to indicate the first physical hole is a physicaldefault strut mounting position; determining that a desired correctioncannot be performed with the physical strut mounted to the firstphysical fixation ring at the physical default strut mounting position;in response to determining that the desired correction cannot beperformed, selecting on the display device, via a user input device, asecond one of the virtual holes, wherein the second virtual holecorresponds to a second physical hole of the first physical fixationring, the second physical hole being a physical non-default strutmounting position; in response to selecting the second virtual hole,updating the display device to display the first portion of the virtualstrut positioned within the second virtual hole; and determining thatthe desired correction can be performed with the physical strut mountedto the first physical fixation ring at the physical non-default strutmounting position.
 2. The method of claim 1, wherein the first virtualhole is directly adjacent to the second virtual hole.
 3. The method ofclaim 1, wherein the physical non-default strut mounting position is afirst physical non-default strut mounting position, and wherein a thirdvirtual hole is positioned between the first virtual hole and the secondvirtual hole, the third virtual hole corresponding to a third physicalhole of the first physical ring, the third physical hole being a secondphysical non-default strut mounting position.
 4. The method of claim 1,further comprising, in response to determining that the desiredcorrection can be performed, mounting the physical strut to the firstphysical fixation ring at the physical non-default strut mountingposition.
 5. The method of claim 1, further comprising, afterdetermining that the desired correction cannot be performed,highlighting on the display device all valid virtual non-default strutmounting positions that correspond to the virtual default strut mountingposition.
 6. The method of claim 1, wherein the first virtual fixationring is a proximal virtual fixation ring, and the first portion of thevirtual strut is a proximal portion of the virtual strut.
 7. The methodof claim 6, further comprising: displaying on the display device avirtual distal fixation ring including a plurality of virtual distalholes extending through the virtual distal fixation ring.
 8. The methodof claim 7, wherein the distal virtual fixation ring corresponds to asecond physical fixation ring, the second physical fixation ring being adistal physical fixation ring, the first physical fixation ring being aproximal physical fixation ring.
 9. The method of claim 8, wherein theplurality of virtual distal holes correspond to a plurality of physicaldistal holes in the distal physical fixation ring.
 10. The method ofclaim 9, further comprising: displaying on the display device a virtualrepresentation of a distal portion of the strut positioned within afirst one of the virtual distal holes.
 11. The method of claim 10,wherein the first virtual distal hole corresponds to a first one of thephysical distal holes, the distal physical fixation ring including asecond indicator adjacent to the first physical distal hole to indicatethe first physical distal hole is a physical default distal strutmounting position.
 12. The method of claim 11, further comprising, inresponse to determining that the desired correction can be performed,mounting the physical strut to the proximal physical fixation ring atthe physical non-default strut mounting position, and mounting thephysical strut to the distal fixation ring at the physical defaultdistal strut mounting position.
 13. The method of claim 12, furthercomprising coupling fix additional physical struts to the proximalphysical fixation ring and to the physical distal fixation ring so thatat total of six physical struts connect the proximal physical fixationring to the physical distal fixation ring.
 14. The method of claim 13,wherein the physical proximal fixation ring includes a first group ofphysical holes that are aligned in a first circumferential row.
 15. Themethod of claim 14, wherein the physical proximal fixation ring includesa plurality of tabs extending radially outward of the firstcircumferential row.
 16. The method of claim 15, wherein the physicalproximal fixation ring includes a second group of physical holes thatare aligned in a second circumferential row positioned within theplurality of tabs.
 17. The method of claim 1, wherein the first virtualfixation ring is a distal virtual fixation ring, and the first portionof the virtual strut is a distal portion of the virtual strut.
 18. Themethod of claim 17, further comprising: displaying on the display devicea virtual proximal fixation ring including a plurality of virtualproximal holes extending through the virtual proximal fixation ring. 19.The method of claim 18, wherein the proximal virtual fixation ringcorresponds to a second physical fixation ring, the second physicalfixation ring being a proximal physical fixation ring, the firstphysical fixation ring being a distal physical fixation ring.
 20. Themethod of claim 19, wherein the plurality of virtual proximal holescorrespond to a plurality of physical proximal holes in the proximalphysical fixation ring.